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ThesisItem Embargo Biochemical characterization and gene expression analysis of pulp pigmentation specific genes in pummelo(Punjab Agricultural University, Ludhiana, 2023) Mandeep Kaur; Rattanpal, H.S.The present study aimed at morphological and biochemical characterization of pummelo genotypes grown under the subtropical condition of North India along with gene expression analysis for pulp colour developmental genes involved in carotenoid biosynthesis. Morphological characters of pummelo genotypes were studied as per International Plant Genetic Resources Institute, Italy descriptors for citrus. A wide range of genetic diversity was observed for fruit length (102.1-158.6 mm), fruit diameter (98.8-146.7 mm), peel thickness (10.9-21.8 mm), fruit weight (427.2-1150.0 g), peel weight (179.7-526.2 g), juice content (76.6-221.3 ml) and seed number per fruit (51.0-132.0) whereas, a relatively narrow range of genetic diversity was observed for flower length (30.0-41.4 mm), number of petals (4-5) and the number of segments (15.0-20.0). The highest fruit size was recorded in NRCC Pummelo5 and PTF-1. Basic fruit quality attributes and components of the antioxidant defense mechanism were estimated colorimetrically. Among biochemical attributes (total soluble sugars, titratable acidity, total sugars, sucrose and reducing sugars), NRCC Pummelo-3 and PTF-4 had the best quality fruits on account of the maximum sugar-acid ratio. Relatively higher content of vitamin C, total phenols, total flavonoids, o-dihydroxy phenols and total antioxidant capacity (DPPH and activity of antioxidant enzymes - superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) was recorded in PTF-4 and NRCC Pummelo3. With respect to the volatile composition of pummelo genotypes as determined by GC-MS analysis, a total of thirty and sixty one volatile compounds were identified in pummelo peel oil and juice, respectively. Limonene was observed as the most predominant compound in pummelo peel oil as well as juice. Additionally, the expression of pulp pigmentation-specific genes in pummelo genotypes including pink-fleshed (NRCC Pummelo-3 and PTF-4) and white-fleshed (Local) was studied. The genes upstream of the lycopene biosynthesis (HDS, HDR, DXS, DXR, PDS, PSY, ZDS, ZISO, CRTISO and PLIS) were up-regulated whereas the genes downstream of the lycopene biosynthesis (ε-LCY, ε-CHX, β-CHX, CCD1, CCD4, AAO3, A1CYP707, A3CYP707 and A4CYP707) were down-regulated. Relative expression of carotenoid biosynthesis genes was the highest in NRCC Pummelo-3 than PTF-4 with respect to Local genotype. The information generated may assist fruit breeders to shortlist the genotypes in hybridization programs for the development of nutritionally-enriched cultivars.
